C++

参考

<map>

multimap

public member function
<map>

std::multimap::operator=

copy (1)
 multimap& operator= (const multimap& x);
copy (1)
multimap& operator= (const multimap& x);
move (2)
multimap& operator= (multimap&& x);
initializer list (3)
multimap& operator= (initializer_list<value_type> il);
Copy container content
Assigns new contents to the container, replacing its current content.

Copies all the elements from x into the container, changing its size accordingly.

The container preserves its current allocator, which is used to allocate additional storage if needed.
The copy assignment (1) copies all the elements from x into the container (with x preserving its contents).

The move assignment (2) moves the elements of x into the container (x is left in an unspecified but valid state).

The initializer list assignment (3) copies the elements of il into the container.

The new container size is the same as the size of x (or il) before the call.

The container preserves its current allocator, except if the allocator traits indicate x's allocator should propagate. This allocator is used (through its traits) to allocate or deallocate if there are changes in storage requirements, and to construct or destroy elements, if needed.

The elements stored in the container before the call are either assigned to or destroyed.

参数

x
A multimap object of the same type (i.e., with the same template parameters,key, T, Compare和Alloc).
il
一个 initializer_list 对象。编译器将自动从初始化列表声明器创建此类对象。
成员类型value_typeis the type of the elements in the container, defined in multimap as an alias ofpair<const key_type, mapped_type>(see multimap member types).

返回值

*this

示例

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// assignment operator with multimaps
#include <iostream>
#include <map>

int main ()
{
  std::multimap<char,int> foo,bar;

  foo.insert(std::make_pair('x',32));
  foo.insert(std::make_pair('y',64));
  foo.insert(std::make_pair('y',96));
  foo.insert(std::make_pair('z',128));

  bar = foo;                  // bar now contains 4 ints
  foo.clear();                // and first is now empty

  std::cout << "Size of foo: " << foo.size() << '\n';
  std::cout << "Size of bar: " << bar.size() << '\n';
  return 0;
}
输出
Size of foo: 0
Size of bar: 4


复杂度

For the copy assignment (1): Linear in sizes (destructions, copies).
For the move assignment (2): Linear in current container size (destructions).*
For the initializer list assignment (3): Up to logarithmic in sizes (destructions, move-assignments) -- linear if il is already sorted.
* Additional complexity for assignments if allocators do not propagate.

迭代器有效性

All iterators, references and pointers related to this container are invalidated.

In the move assignment, iterators, pointers and references referring to elements in x are also invalidated.

数据竞争

All copied elements are accessed.
The move assignment (2) modifies x.
The container and all its elements are modified.

异常安全

Basic guarantee: if an exception is thrown, the container is in a valid state.
If allocator_traits::construct is not supported with the appropriate arguments for the element constructions, or ifvalue_typeis not copy assignable (or move assignable for (2)), it causes undefined behavior.

另见

multimap::insert
插入元素 (公开成员函数)
multimap::find
获取指向元素的迭代器 (公共成员函数)
multimap::multimap
Construct multimap (public member function)